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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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International Journal of Concrete Structures and Materials
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Journal DOI :
Korea Concrete Institute
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Volume & Issues
Volume 5, Issue 2 - Dec 2011
Volume 5, Issue 1 - Jun 2011
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Mechanical Properties of Cement Mortar: Development of Structure-Property Relationships
Ghebrab, Tewodros Tekeste ; Soroushian, Parviz ;
International Journal of Concrete Structures and Materials, volume 5, issue 1, 2011, Pages 3~10
DOI : 10.4334/IJCSM.2011.5.1.003
Theoretical models for prediction of the mechanical properties of cement mortar are developed based on the morphology and interactions of cement hydration products, capillary pores and microcracks. The models account for intermolecular interactions involving the nano-scale calcium silicate hydrate (C-S-H) constituents of hydration products, and consider the effects of capillary pores as well as the microcracks within the hydrated cement paste and at the interfacial transition zone (ITZ). Cement mortar was modeled as a three-phase material composed of hydrated cement paste, fine aggregates and ITZ. The Hashin's bound model was used to predict the elastic modulus of mortar as a three-phase composite. Theoretical evaluation of fracture toughness indicated that the frictional pullout of fine aggregates makes major contribution to the fracture energy of cement mortar. Linear fracture mechanics principles were used to model the tensile strength of mortar. The predictions of theoretical models compared reasonably with empirical values.
Prediction of Durability for RC Columns with Crack and Joint under Carbonation Based on Probabilistic Approach
Kwon, Seung-Jun ; Na, Ung-Jin ;
International Journal of Concrete Structures and Materials, volume 5, issue 1, 2011, Pages 11~18
DOI : 10.4334/IJCSM.2011.5.1.011
Carbonation in RC (reinforced concrete) structure is considered as one of the most critical deteriorations in urban cities. Although RC column has one mix condition, carbonation depth is measured spatially differently due to its various environmental and internal conditions such as sound, cracked, and joint concrete. In this paper, field investigation was performed for 27 RC columns subjected to carbonation for eighteen years. Through this investigation, carbonation distribution in sound, cracked, and joint concrete were derived with crack mappings. Considering each related area and calculated PDF (probability of durability failure) of sound, cracked, and joint concrete through Monte Carlo Simulation (MCS), repairing timings for RC columns are derived based on several IPDF (intended probability of durability failure) of 1, 3, and 5%. The technique of equivalent probability including carbonation behaviors which are obtained from different conditions can provide the reasonable repairing strategy and the priority order for repairing in a given traffic service area.
Dynamic Response of Reinforced Concrete Beams Following Instantaneous Removal of a Bearing Column
Tian, Ying ; Su, Youpo ;
International Journal of Concrete Structures and Materials, volume 5, issue 1, 2011, Pages 19~28
DOI : 10.4334/IJCSM.2011.5.1.019
This paper documents an experimental study of dynamic response of reinforced concrete beams following instantaneous removal of a bearing column. Four half-scale specimens representing two-span beam bridging across the removed column were tested. The test boundary conditions simulated rotational and longitudinal restraints imposed on a frame beam by the neighboring structural components. The gravity loads were simulated by attaching mass blocks on the beams at three locations. Dynamic loading effects due to sudden removal of a column were simulated by quickly releasing the supporting force at the middle of the specimens. The experimental study investigated the load-carrying capacity of beams restrained longitudinally at the boundaries and dynamic impact on forces. The tests confirmed the extra flexural strength provided by compressive arch action under dynamic loading. The tests also indicated that the dynamic amplification effects on forces were much lower than that assumed in the current design guideline for progressive collapse.
Model of Least Square Support Vector Machine (LSSVM) for Prediction of Fracture Parameters of Concrete
Kulkrni, Kallyan S. ; Kim, Doo-Kie ; Sekar, S.K. ; Samui, Pijush ;
International Journal of Concrete Structures and Materials, volume 5, issue 1, 2011, Pages 29~33
DOI : 10.4334/IJCSM.2011.5.1.029
This article employs Least Square Support Vector Machine (LSSVM) for determination of fracture parameters of concrete: critical stress intensity factor (
) and the critical crack tip opening displacement (
). LSSVM that is firmly based on the theory of statistical learning theory uses regression technique. The results are compared with a widely used Artificial Neural Network (ANN) Models of LSSVM have been developed for prediction of
, and then a sensitivity analysis has been performed to investigate the importance of the input parameters. Equations have been also developed for determination of
. The developed LSSVM also gives error bar. The results show that the developed model of LSSVM is very predictable in order to determine fracture parameters of concrete.
Design Equation for Punching Shear Capacity of SFRC Slabs
Higashiyama, Hiroshi ; Ota, Akari ; Mizukoshi, Mutsumi ;
International Journal of Concrete Structures and Materials, volume 5, issue 1, 2011, Pages 35~42
DOI : 10.4334/IJCSM.2011.5.1.035
In this paper, a design equation for the punching shear capacity of steel fiber reinforced concrete (SFRC) slabs is proposed based on the Japan Society of Civil Engineers (JSCE) standard specifications. Addition of steel fibers into concrete improves mechanical behavior, ductility, and fatigue strength of concrete. Previous studies have demonstrated the effectiveness of fiber reinforcement in improving the shear behavior of reinforced concrete slabs. In this study, twelve SFRC slabs using hooked-ends type steel fibers are tested with varying fiber dosage, slab thickness, steel reinforcement ratio, and compressive strength. Furthermore, test data conducted by earlier researchers are involved to verify the proposed design equation. The proposed design equation addresses the fiber pull-out strength and the critical shear perimeter changed by the fiber factor. Consequently, it is confirmed that the proposed design equation can predict the punching shear capacity of SFRC slabs with an applicable accuracy.
Composite Strips with Various Anchor Systems for Retrofitting Concrete Beams
Yoshitake, Isamu ; Yumikura, Keiyu ; Mimura, Yoichi ; Kim, Yail-J. ;
International Journal of Concrete Structures and Materials, volume 5, issue 1, 2011, Pages 43~48
DOI : 10.4334/IJCSM.2011.5.1.043
This paper presents the performance of anchor systems for reinforced concrete beams retrofitted with carbon fiber reinforced polymer (CFRP) strips. Nine simply-supported beams are tested with various anchor systems such as steel hooks, steel plates with anchor bolts, CFRP anchor plates, and near-surface mounted (NSM) CFRP strip. The effects of these anchors on the behavior of the retrofitted beams are discussed, including load-carrying capacity, failure modes, and ductility characteristics. Test results indicate that end-anchorage is an important parameter when a CFRP-retrofit design is conducted. Mechanical bolts and NSM CRFP anchors are recommended.
Size Effect of Axial Compressive Strength of CFRP Confined Concrete Cylinders
Akogbe, Romuald-Kokou ; Liang, Meng ; Wu, Zhi-Min ;
International Journal of Concrete Structures and Materials, volume 5, issue 1, 2011, Pages 49~55
DOI : 10.4334/IJCSM.2011.5.1.049
The main objective of this investigation is to study size effect on compressive strength of CFRP confined concrete cylinders subjected to axial compressive loading. In total 24 concrete cylinders with different sizes were tested, small specimens with a diameter of 100 mm and a height of 200 mm, medium specimens with a diameter of 200 mm and a height of 400 mm, and big specimens with a diameter of 300 mm and a height of 600 mm. The lateral confining pressure of each specimen is the same and from that hypothesis the small specimens were confined with one layer of CFRP, medium and big specimens were performed by two and three layers of CFRP respectively. Test results indicate a significant enhancement in compressive strength for all confined specimens, and moreover, the compressive strengths of small and medium specimens are almost the same while a bit lower for big specimens. These results permit to conclude that there is no size effect on compressive strength of confined specimens regardless of cylinder dimension.
Joint Shear Behavior Prediction for RC Beam-Column Connections
LaFave, James M. ; Kim, Jae-Hong ;
International Journal of Concrete Structures and Materials, volume 5, issue 1, 2011, Pages 57~64
DOI : 10.4334/IJCSM.2011.5.1.057
An extensive database has been constructed of reinforced concrete (RC) beam-column connection tests subjected to cyclic lateral loading. All cases within the database experienced joint shear failure, either in conjunction with or without yielding of longitudinal beam reinforcement. Using the experimental database, envelope curves of joint shear stress vs. joint shear strain behavior have been created by connecting key points such as cracking, yielding, and peak loading. Various prediction approaches for RC joint shear behavior are discussed using the constructed experimental database. RC joint shear strength and deformation models are first presented using the database in conjunction with a Bayesian parameter estimation method, and then a complete model applicable to the full range of RC joint shear behavior is suggested. An RC joint shear prediction model following a U.S. standard is next summarized and evaluated. Finally, a particular joint shear prediction model using basic joint shear resistance mechanisms is described and for the first time critically assessed.
Effectiveness of Calcium Nitrite in Retarding Corrosion of Steel in Concrete
Abosrra, L. ; Youseffi, M. ; Ashour, A.F. ;
International Journal of Concrete Structures and Materials, volume 5, issue 1, 2011, Pages 65~73
DOI : 10.4334/IJCSM.2011.5.1.065
Corrosion of steel bars embedded in concrete admixed with 0%, 2% and 4% calcium nitrite (CN), having compressive strengths of 20 and 46 MPa was investigated. Reinforced concrete specimens were immersed in 3% NaCl solutions for 1, 7 and 15 days where 0.4A external current was applied to accelerate the chemical reactions. Corrosion rate was measured by retrieving electrochemical data via potentiodynamic polarization technique. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel-concrete bond characteristics. Experimental results showed that corrosion rate of steel bars and steel-concrete bond strength were dependent on concrete strength, amount of CN added and accelerated corrosion period. As concrete strength increased from 20 to 46 MPa, corrosion rate of embedded steel decreased. The addition of 2% CN to concrete of 20 MPa was not effective in retarding corrosion of steel at long time of exposure. However, the combination of higher strength concrete and 2% or 4% CN appear to be a desirable approach to reduce the effect of chloride-induced corrosion of steel reinforcement. After 1 day of corrosion acceleration, specimens without CN showed higher bond strength in both concrete mixes than those with CN. After 7 and 15 days of exposure, the higher concentration of CN, the higher bond strength in both concrete mixes achieved, except for the concrete specimen of 20 MPa compressive strength with 2% CN that recorded the highest deterioration in bond strength at 15 days of exposure.